Field of the Invention
The present invention relates to a reaction mixture and a biotechnological method of producing alcohols including higher alcohols from a carbon source in aerobic conditions. In particular, the mixture and method relates to a biotechnological production of at least one alcohol in the presence of oxygen and young cells.
Discussion of the Background
Biotechnological methods of producing alcohols, particularly ethanol are well known in the art. Especially the use of acetogenic bacteria on various carbon sources to produce ethanol and/or acetate is well known. However, in most cases, the production of alcohols can only be successfully carried out in the absence of oxygen. This phenomenon is confirmed at least by Brioukhanov, 2006, Imlay, 2006, Lan, 2013 and the like where it is shown that acetogenic bacteria do not successfully produce ethanol in aerobic conditions. Therefore, in the current methods known in the art, carbon substrates comprising oxygen, such as waste gases from steel mills are first processed to remove the oxygen before they are introduced to the acetogenic cells for ethanol and/or acetate production. The oxygen separation step makes the process more expensive and time consuming. Further, there may be some loss in the raw materials during this step of separation.
There is thus a need in the art for a means of producing ethanol and/or acetate in the presence of oxygen. Ethanol may then be used as a raw material for production of higher carbon compounds such as alcohol, acids and the like.
For example, butanol and higher alcohols have several uses including being used as fuel. For example, butanol in the future can replace gasoline as the energy contents of the two fuels are nearly the same. Further, butanol has several other superior properties as an alternative fuel when compared to ethanol. These include butanol having higher energy content, butanol being less “evaporative” than ethanol or gasoline and butanol being easily transportable compared to ethanol. For these reasons and more, there is already an existing potential market for butanol and/or related higher alcohols. Butanol and other higher alcohols are also used as industrial solvents.
Currently, butanol and other higher alcohols are primarily manufactured from petroleum. These compounds are obtained by cracking gasoline or petroleum which is bad for the environment. Also, since the costs for these starting materials will be linked to the price of petroleum, with the expected increase in petroleum prices in the future, butanol and other higher alcohol prices may also increase relative to the increase in the petroleum prices.
Historically (1900s-1950s), biobutanol was manufactured from corn and molasses in a fermentation process that also produced acetone and ethanol and was known as an ABE (acetone, butanol, ethanol) fermentation typically with certain butanol-producing bacteria such as Clostridium acetobutylicum and Clostridium beijerinckii. This method has recently gained popularity again with renewed interest in green energy. However, the “cornstarch butanol production” process requires a number of energy-consuming steps including agricultural corn-crop cultivation, corn-grain harvesting, corn-grain starch processing, and starch-to-sugar-to-butanol fermentation. The “cornstarch butanol production” process could also probably cost nearly as much energy as the energy value of its product butanol.
The Alfol® Alcohol Process is a method used to producing higher alcohols from ethylene using an organoaluminium catalyst. The reaction produces linear long chain primary alcohols (C2-C28). The process uses an aluminum catalyst to oligomerize ethylene and allow the resulting alkyl group to be oxygenated. However, this method yields a wide spectrum of alcohols and the distribution pattern is maintained. This constant pattern limits the ability of the producer to make only the specific alcohol range that is in highest demand or has the best economic value. Also, the gases needed in the reaction have to be very clean and a distinct composition of the gases is needed for the reaction to be successfully carried out.
WO2009100434 also describes an indirect method of producing butanol and hexanol from a carbohydrate. The method includes a homoacetogenic fermentation to produce an acetic acid intermediate which is then chemically converted to ethanol. The ethanol and a remaining portion of the acetic acid intermediate are then used as a substrate in an acidogenic fermentation to produce butyric and caproic acid intermediates which are then chemically converted to butanol and hexanol. However, this method uses expensive raw material carbohydrates and has two additional process steps, the formation of the esters and the chemical hydrogenation of the esters which make the method not only longer but also results in loss of useful material along the way.
Perez, J. M., 2012 discloses a method of converting short-chain carboxylic acids into their corresponding alcohols in the presence of syngas with the use of Clostridium ljungdahlii. However, short-chain carboxylic acids have to be added as a substrate for the conversion to the corresponding higher alcohol.
The currently available methods of higher alcohol production thus has limitations in mass transfer of the gaseous substrates into fermentation broth, lower productivity, and lower concentrations of end products, resulting in higher energy costs for product purification.